1. Field of the Invention
The present invention relates to radio communication systems utilizing radio transmission towers and, more particularly, to such a system which utilizes a first radio transmitter to transmit a received or generated electrical signal from a position on the ground to a radio transceiver positioned in an upper portion of the tower for broadcasting of the electrical signal out from the tower.
2. Setting of the Invention
The long distance transmission of information, such as voice, digital or analog data, utilizing radio frequencies requires a radio transmission tower, an antenna mounted to the tower, a radio transmitter, and a source of electrical power connected to the radio transmitter. The amount of power (in watts) used to transmit or broadcast the electric signal, the height of the tower, and the gain of the antenna all affect the initial cost and obviously the maintenance cost of any radio transmission system. Usually, the electrical signal which is to be transmitted is received at or generated within a ground transmission facility and is then communicated to the transmission antenna on the uppermost portion of the tower by way of a coaxial cable. It has been found that there is substantial power loss in or through the coaxial cable extending from the ground based transmitter to the tower mounted antenna. The amount of such power loss is determined by the diameter and type of the coaxial cable, as well as the frequency of the transmitted signal. For example, a five watt signal sent from the transmitter can lose as much as 70% of its power when measured at the antenna mounted on a 300 ft tower. Further, the use of coaxial cable is expensive from a purchase standpoint and is prone to water damage and shorting caused by rain, wind, and lightening. It is desirable to have a radio communication system which does not require the use of coaxial cable to connect the ground based transmitter to the tower mounted antenna.
Further, the maintenance of a radio transmission system can be very expensive. If there is any maintenance to be done to the coaxial cable and/or the antenna, then a maintenance man has to climb to the top of the tower, which is a dangerous procedure, and thus is very costly. Presently, such a "tower climber" charges approximately $2-$3 per foot to climb the tower which obviously can be extremely expensive even for a relatively short tower, such as 200-300 ft in height. There is a need for a radio communication system which does not utilize coaxial cable, as stated above, and which provides a simple, inexpensive mechanism for maintenance of the antenna without the need for a person to climb the tower or to utilize a large crane to reach the antenna on a short tower.
One radio communication system which does not utilize coaxial cable and protects the antenna from damage is a microwave transmission system where the radio transmitter and antenna are mounted on the ground adjacent a tower. The microwave signals are then directed to or aimed at an angled reflector on the tower so that the microwave signals will bounce off of the reflector and travel to a distant location. Such a microwave system is inoperative with regular radio signals, such as 100-1,000 mHz, because the radio energy at that frequency requires too large of a focusing dish to be practical.